1. Field
The present disclosure relates to a semiconductor device.
2. Description of the Related Art
Active matrix substrates used for liquid crystal displays and the like include, for each pixel, a switching element such as a thin film transistor (hereafter, “TFT”). Such switching elements that have been widely used include a TFT having an amorphous silicon film as an active layer (hereafter, “amorphous silicon TFT”), and a TFT having a polycrystalline silicon film as an active layer (hereafter, “polycrystalline silicon TFT”).
However, such amorphous silicon and polycrystalline silicon serving as the materials for active layers of TFTs have come to be replaced by oxide semiconductors in some cases. The resultant TFTs are referred to as “oxide semiconductor TFTs”. Oxide semiconductors have higher mobility than amorphous silicon. Thus, oxide semiconductor TFTs can function faster than amorphous silicon TFTs. Thus, there are known techniques of using oxide semiconductor TFTs to form driving circuits such as a gate driver and a source driver, as monolithic (integrated) structures on substrates.
Although most of oxide semiconductor TFTs have a bottom gate structure, oxide semiconductor TFTs having a top gate structure have also been proposed (for example, Japanese Unexamined Patent Application Publication No. 2015-195363). Such an oxide semiconductor TFT proposed in Japanese Unexamined Patent Application Publication No. 2015-195363 has an oxide semiconductor layer; a gate electrode disposed above the oxide semiconductor layer (on a side of the oxide semiconductor layer, the side being opposite to the other side facing the substrate) with a gate insulating film disposed between the gate electrode and the oxide semiconductor layer; a source electrode; and a drain electrode. The oxide semiconductor layer, the gate insulating film, and the gate electrode are covered with an interlayer insulating film. The source electrode and the drain electrode are, within openings in the interlayer insulating film, in contact with portions of the oxide semiconductor layer (the portions being referred to as a “source contact region” and a “drain contact region”).